BLOOD-VOLUME REGULATION DURING HEMODIALYSIS

Hemodialysis (HD)-induced hypotension may be precipitated by severe hy povolemia. To avoid the appearance of destabilizing hypovolemias, we h ave developed a biofeedback control system for intradialytic blood Vol ume (BV)-changes modeling, The system, incorporated in a dialysis mach ine, is based on a multivariable closed-loop control with a dependent output variable, the BV changes, and two independent control variables , the ultrafiltration rate (Qf) and dialysate conductivity (DC). The r elative BV changes occurring during HD are measured by an optical devi ce. The Of and DC are continuously adjusted by the control model durin g the treatment to minimize any discrepancies between the ideal target s for the BV, the patient's body weight reductions, and the experiment ally obtained results. The system manages three kinds of errors: in BV changes, the total weight loss, and the sodium balance. The latter is controlled by a dedicated kinetic model that continuously calculates the equivalent DC and, by the end of the session, tends to make the so dium balance the same as the one obtained in conventional HD with cons tant DC. This system's capacity to improve intradialytic hemodynamic t olerance has been assessed in a crossover study of eight highly sympto matic patients. Conventional HD (CHD; period A) was compared with bloo d volume-controlled dialysis sessions (BV-CHD; period B) following a p rotocol with an A1-B-A2 sequence, with each period lasting 1 month. A lower decrease in BV (-10.6%) was obtained during BV-CHD (period B) co mpared with CHD (-12.3% in period Al and -12.5% in period A2). The pre dialysis to postdialysis systolic arterial pressure changes were lower in period B (-12.4%) than in period A (-20% in A1 and -17.5% in A2; P < 0.05) despite similar total Qf and mean treatment times. A signific ant reduction in the number of severe hypotensive episodes (three in p eriod B v 26 in period A1 and 16 in period A2; P < 0.05) and the overa ll incidence of complaints, especially of muscular cramps, was found i n BV-CHD. These results were reflected in a reduced need for therapeut ically administered isotonic saline in each session (60 mL in B v 160 mt in Al and 95 mt in A2; P < 0.05), In conclusion, the proposed biofe edback system for intradialytic BV control may be useful to avoid seve re hypovolemic states, to stabilize BV by modeling its trend, and to a void reaching individual critical BV thresholds in hypotension-prone p atients. (C) 1998 by the National Kidney Foundation, Inc.